Roses are important plants as cut flowers, and their color has been investigated in detail. For example, known examples of anthocyanin-based pigments include cyanidin 3,5-diglucoside, pelargonidin 3,5-diglucoside, cyanidin 3-glucoside, pelargonidin 3-glucoside, peonidin 3,5-diglucoside and peonidin 3-glucoside. The biosynthesis pathways of anthocyanins containing these pigments are known.
In addition, roses that express flavonoid 3′,5′-hydroxylase gene due to genetic recombination (refer to Patent Document 1 and Patent Document 2) produce delphin (also referred to as delphidin 3,5-diglucoside). In this case, the hydroxylation reaction at the 5′ position of the B ring of the flavonoid is thought to take place at the stage of flavanone or dihydroflavonol. Since flavonoid 3′5′-hydroxylase is a kind of cytochrome P450 present in endoplasmic reticulum, this hydroxylation is assumed to occur on endoplasmic reticulum. In addition to not having a sequence such as a signal peptide, since enzymes such as anthocyanidin glycosyltransferase, which catalyze the biosynthesis reactions of anthocyanins, are soluble proteins, they are present in the cell cytoplasm. Anthocyanins are transported into vacuoles by a pump following glycosylation.
On the other hand, compound rosacyanins (see FIG. 1) have been reported to be present in at least some roses, and the structures of rosacyanins such as rosacyanin A1, rosacyanin B and rosacyanin A2 have been determined (see, for example, Patent Document 3 or Non-Patent Document 1).
Since rosacyanins have a cyanidin backbone in a portion of their structure, there the possibility that they are synthesized based on cyanidin, a common precursor with cyanidin or an analog of cyanidin. However, since this remains to be only speculation, what types of substances are actually used as precursors and what types of pathways are used in synthesis have yet to be clearly determined.
On the other hand, delphinidin is synthesized instead of a portion of the cyanidin in roses in which flavonoid 3′,5′-hydroxylase gene is expressed as a result of genetic recombination as previously described. If the aforementioned hypothesis regarding the rosacyanin synthesis pathway, namely that rosacyanin is synthesized by using cyanidin as a precursor, is correct, then rosacyanin would not be synthesized in these genetically modified roses in which cyanidin serving as precursor is essentially absent.
When the inventors of the present invention conducted an analysis to obtain findings regarding rosacyanin synthesis using the aforementioned genetically modified roses that hardly contain any cyanidin or have a considerably decreased cyanidin content in comparison with a host as described in Patent Document 1 or Patent Document 2, contrary to expectations, a novel compound was found to be present having a chemical structure that clearly differed from that of rosacyanins inherently possessed by roses. Moreover, this novel compound was clearly determined to be uniquely present in roses in which flavonoid 3′,5′-hydroxylase gene was expressed by genetic recombination, thereby leading to completion of the present invention.